YouTubers have been enjoying some spectacular footage of the disintegration of a Danish wind turbine which ended up a bit broken after its brakes failed:
The suicidal turbine was located at Hornslet near Aarhus. According to the Telegraph, the 60m-high structure was ten years old and manufactured by Vestas. Engineers who …

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Explosive blades

I understood that the blades on big wind turbines like this are on synchronised* explosive couplings so that the blades can be ejected in situations like this where the rotational speed gets too high? (*Hence why they all fly off simultaneously)

Fazed

This was covered on Fazed.net the other day...at least one of the comments posted by someone who knew what they were talking about mention the fact that THREE safety systems had to have failed in order for the turbine to over-rev, causing muchos damage!

Bloody impressive videos mind :D

[quote]

There is a lot of incorrect or misleading information in this comment thread, so let me try to clarify a few things about turbine operation and safety.

This is definitely not fake, and that is a textbook example of turbine structural failure due to overspeed. That speed is far outside the design parameters, and the forces on the structure far beyond the design as well. Asking it to be able to survive that is like asking for your car to not be crushed when you crash it into a wall at 60 mph.

Turbine rotor speed is generally controlled in three basic ways. The first is simply the resistance of the generator itself. However if the generator fails or is disconnected from the power grid this source of resistance fails as well.

The second speed control method is by changing the aerodynamics of the rotor. On most modern pitch regulated turbines this involves changing the pitch of the rotor blades into the wind. When the blades are pitched 90 degrees out of the wind they generate essentially zero rotational force. On simpler stall regulated machines, which cannot adjust blade pitch, a tip brake is activated; the last few feet of the blades are pushed out a few inches and turned out of the wind. This achieves a similar aerodynamic effect. Either method is usually enough to stop a turbine fairly quickly, and this is the primary control mechanism. These systems have either springs or hydraulic accumulators and should automatically activate in case of other systems failure.

The third method is a mechanical brake. This is generally a massive disk brake, and may be mounted either on the low-speed input shaft, or, more commonly, on the high speed shaft connecting the gearbox to the generator. This brake is typically used as a parking brake during maintenance, but can be activated as an emergency brake as well.

Overspeed like this would require the turbine to be offline and not generating power, and for both the aerodynamic and mechanical brakes to fail. It can happen, but is very rare, and I am extremely curious as to exactly how this happened.

As to the fiberglass comment: the most common turbine blade material is glass fiber reinforced plastic. Carbon fiber is being used sometimes, but not often. Early turbines used steel blades, but their weight is just too high for today's large machines. The construction is somewhat like an airplane wing.

The towers are made of steel, if that gives you an idea of just how much energy was released when that thing finally gave way.

Nik282000 is wrong on his/her first point. The blades on almost all modern large turbines can turn completely out of the wind, and this is the primary braking mechanism.

And some general information on speed:

Most turbines shut down when wind speeds reach 25 meters per second (56 mph). Some shut down at 20 meters per second (45 mph). They can survive much higher wind speeds when they are not running.

Rotational speeds vary by model but generally range from 10 to 20 revolutions per minute. 15 RPM is a fairly common number. Most turbine models rotate at one or two fixed speeds. GE turbines have more sophisticated power electronics (and a patent) that allows them to vary their rotational speed as wind conditions change.

Think of the children!!

Last time I went through Greenock (I don't know what I did wrong either), I noticed a turbine in the grounds of a new school which is being built. Let's hope the Entegrity turbine doesn't suffer the same fate and take a few West of Scotland schoolkids out.

Hopefully the 9/11 truthers...

Bloody hell!

Had never thought about what would happen to one of those if it 'ran away', definitely the right course of action for the engineers was to leg it and capture it for posterity and post it on You Tube! :)

Die Hippie, Die

@William Clark

obviosuley you never played with lego moters as a child

if one of the waight matched blades gos the uneven spinwill cause it all to disgentrage v soon after cos of thje exisive speen the energy involved made v soon to be undecitable with the footage we have

@Jason Aspinall, Gordon Jahn

The resistance of the generator is varied with nothing more exotic than a gear box.

This should be familiar to everyone who have ever applied "engine brake".

@Gordon Jahn:

That really sounds terrifying!

Considering that Vestas (the manufacturer of the wind turbine) suspects that the failure was due to poor maintenance - and we all know how high "more money to maintenance" ranks on the political agenda...

Black chopper - because this incident will be completely misrepresented in the energy debate to suit the point of view of the government.

Imagine if...

One of those bits had flown off and hit another turbine, causing it to disintegrate and then much like a domino affect, bring the entire field of brand new just installed that morning turbines crashing to the ground.

Gordon Jahn + Engineering Talent...

Whoever gets any contract for the creation of new Nuclear Power plant will not use local engineering talent as you put it. They will, as they always have done, apply the template already used throughout their other installations. Some locals will work there, and some locals will help build it. The higher paid jobs, design and engineering management will not be local.

Scotland and the rest of the uk are hemoraging engineering people because the UAE, NZ, etc... have the money to pay for things, and UK engineers are regarded as the best in the world. That's why I'll be saying cheerio to my brother and family just as soon as he graduates.

Vertical Blades

I read somewhere previously, possibly the Reg, that the blades on these turbines are very difficult to build and construct and maintain their structural integrity, and that someone had proposed or designed or prototyped a generator that was a set of blades which were essentially parallel to the mast around which they were rotating. Apparenlty they could much better withstand higher wind speeds and were easier to build and maintain than the windmill style turbines we have now?

Am I imagning things? Or did that idea turn out to be a steaming heap of poopy?

Seen this before in the 80's, it's nothing new.

I used to work for a company called WTG Energy Systems in the early eighties. We had 3) 250 KW wind turbines in Vermont, USA and the blade spars back then were made of steel and the hub made of ductile iron. Work hardening of the root of one of the 3 blade spars caused it to become brittle and eventually fail. The 3.5 ton steel blade flew 250 ft and dug a trench 4 ft deep in frozen ground for a distance of 50 to 80 ft. When the first balde broke, the hub broke and one of the blade swung and hit the tower, bending the structural steel leg some 6 feet where it hit.

Our company's design had a disk brake (same brakes that stop a B52 Bomber) on the back side of the gearbox and the wing tips automatically rotated perpendicular to the axis of rotation to slow the turbine down if the anemometer sensed too high a wind speed or any imbalance in the rotor.

Anyone stupid enough to use explosive bolts to blow the blades off in an overspeed scenario would have one helluva shock when lightning hits their wind turbine, which happens in nearly every storm. Not even considering that the blades creat a TREMENDOUS static electricity charge by merely rotating in the air.

The part that was hilarious was the fact that our project manager was in the control building in between the legs of the steel support tower along with the customer, who were a silent order of monks looking for an apocalypse proof source of electrical power. Our project manager let loose a stream of profanities when the blade broke and the monks broke their vow of silence though in a less profane manner. No one mentioned if the toilet paper had to be passed around in the aftermath but I'm pretty sure it did.

The British connection of the story is that we had a similar turbine sold to the power company in Cardiff Wales. I wonder if it still exists anymore.

Failsafe aerobrakes

Where are the failsafe aerobrakes that pop out at the wingtips when the rotational speed gets too high? Heck, it could be a simple glass plate, with a calibrated weight that breaks the glass, and a little parachute pops out. This should happen when the speed is above the operational limits, but below the damage limit. Duh.

Look no radioactive pollution

A potentially terrible physical accident - but at least there's no radioactive pollution which, in the case of nuclear accidents at Three Mile Island, Windscale and Chernobyl (to name but 3) has permanently damaged the gene pool causing birth defects and cancers not only then, now but into the future!

re: Explosive blades

That has to be the biggest load of Bollocks ever.. The blades are not explosive they are not desigend to fail simultaeniously. That is all made up garbage. next you'll be saying cars are packed with explosives so they can be ejected from the road proir to any accidents.

what happens is this: the blades are all built to the same specs and are similar, at overspeed one blade fails, (usually between 180-225 Degrees due to gravity loading) at failure a shockwave travels through the whole structure which is enough to cause the other (already highly loaded) blades to fail also, and even enough to wrench the mast apart.

if you watch in slo-mo this is exactly what happens in this case.

If the shockwave is not for it to catastrophically fail then it will shake itself to bits within minutes as it is completely unbalanced.

The only place explosive bolts are used is in blade off tests, where failure is desired.

Wow

Aircraft have to be maintained too

Modern wind turbine blades are similar to aircraft wing technology. Given the number of these turbines now installed in various parts of the world it's almost inevitable that a few are tested to destruction by human nature being what it is - in this case the apparent neglect of basic maintenance.

Consider how the air travel industry made it less likely that aircraft would fall out of the sky. A crash investigation and maintenance quality assurance culture was developed over a number of decades, such that one engineer can not tighten a bolt without another signing a form to say they had checked what the first engineer has done. The wind energy industry is at a similar stage of development to the aircraft operations industry in the nineteen thirties - they had proven the concept 20 years before, ironed out some of the worst problems in the first couple of decades and gone into mass production but without developing a QA bureacracy sufficient to keep adequate checks on the maintenance of many potentially dangerous engineering structures.

Large windfarms are more likely to be maintained properly than isolated turbines operated by amateurs whose main income come from other sources. I suspect that in the larger windfarms the machines are sited far enough apart that cascade failures are inherently unlikely but can't state this with any certainty. It's an interesting question, though the degree of neglect needed for this to happen seems much less likely in a big windfarm.

Van?

Why is that van parked so close to the wind turbine when they knew it was going to fail? In the second video, you can see a big poof of dirt right at the moment of failure, and it appears pretty close to the van. After that, it looks like the support tower for the turbine falls pretty close to the van as well.

Smashing

@Tim, Niall, some basic wind facts

Tim Spence: The energy in the wind scales as the cube of the wind speed, so you wouldn't just need to go from 1 generator to 2 to 3, but from 1 to 4 to 9 and so on. The hub and gearbox to handle 9 generators worth of torque would be so bulky and have so much resistance that at normal (1 generator) wind speed, they'd eat your efficiency. Wind machines are designed for a specific range of speeds. Below that, there's not enough energy in the wind for them to bother with, and above that, there's so much it's nearly impossible to capture.

Niall: Vertical axis wind turbines have a tougher time than horizontal-axis machines, for one simple reason: On each revolution, every blade goes from facing into the wind, to facing against it, to facing away from it, to facing against it, and back into it again. This creates oscillating stresses on each blade, which are much harder to withstand than the constant stress experienced by the blades of a horizontal-axis turbine.

And yes, the force of gravity does technically oscillate, relative to the blades of a horizontal axis turbine, but gravity is minor compared to the other forces at play in such a machine. Proponents of vertical-axis machines seem convinced that a giant conspiracy, not the laws of physics, is to blame for the thousand-year dominance of horizontal-axis turbines.

Personally witnessed similar items.

Wind turbine blades are designed to stand up to some incredibly nasty conditions for many years without failure. Case and point are the windfarms East-South-East of Tehachapi California where they get some wickedly high winds but are also at the edge of a desert. The blades there get baked in the 110+ degree temps and alternately frozen when it snows (which has happened in the course of a day). Even with these conditions, blade failures are incredibly rare.

As mentioned previously by several people, the turbines by default are designed to pitch the blades out of the wind or rotate the tips 90 degrees to serve as airbrakes. Alternately turbines can turn the entire nacel out of the wind to keep things from falling apart. I have seen this where the brakes failed on a turbine and power to the generator was lost but there was still power to the other electronics and an operator went to the control box (inside the tower) and rotated the nacel 90 degrees out of the wind and once the turbine had stopped, the blades were secured to the tower and a crew went up and replaced the braking system.

Too bad the braking system didn't catch fire before failing... That's always fun to watch an out of control turbine that happens to be on fire. Nothing like flaming fiberglass bits gently floating in the wind...

If someone has a higher quality vid, it would be interesting to calculate the tip speed of the blades. There have been recorded instances of the tips breaking the sound barrier (a few tens of RPM 20m+ out = a lot of speed) and the blades simply shatter from the tip in (do a frame by frame about 6 seconds into the second video) and then that throws the ballance of the entire system off tweaking the tower which shears at the joints (it looks like a 3 piece tower from the size and the way it fell apart in the vid).

@Niall

They tried to make quasi-vertical blade turbines a long time ago where there was a vertical central shaft and two "blades" bowed out on opposite sides. While they certainly looked novel and could work with wind from any direction, they could not start on their own (they needed a push start basically) and required constantly high winds to be effective. Combine that with the fact that you needed a lot of space for the guy wires and received little electricity in return, well, basically they were giant pieces of crap. The company that put "egg-beaters" in Tehachapi went defunct many years ago and all the machines have been scrapped and replaced with traditional turbines after the property was bought by another windfarm.

More info: http://en.wikipedia.org/wiki/Darrieus_wind_turbine

Paris, cause she hasn't done anything spectacularly stupid lately and can use the attention...

Not the first and not the last

I have worked for Vestas (in fact I have been to the main offices in Aarhus too), and having been involved in a few wind farms I can confirm that the turbines in question do have the three features mentioned. Also when communication is lost the PLC they should shutdown and operate the emergency brake system. However some engineers have commented that sometimes this breaking system can become faulty due to the conditions they work in/under. As this is onland I can't comment on the conponents used (I work with the offshore ones which are slightly different due to the marine enviroument).

However where man and machine are involved it is often proven to be a missed failure during inspection of man made fault which is the reason. Vestas engineers are very well trained (I know I took part in a fair bit myself) but they are only human and when you arrive to something like that you can do nothing but sit back and watch.

Surprised they left the Van that close though.. Looks like an old V52 too...

I'm a little surprised that the video made it onto TouTube however as this is not the first and Vestas have managed to keep the others off the internet.

To keep it in context they are not the only company that has suffered problems and Wind Turbines are still very much an experimental way of harnessing renewalable energy.

Explosive Bolts on Rotors

This probably came from someone who saw a documentary in the late 70s in which an experimental upward seat ejection escape system for helicopters was shown. I recall the test rig had four blades that let go in two opposed pairs to facilitate pilot ejection sans Cuisinart Effect.

When it worked.

Such a mechanism would never be used where a rotating Blade of Death would be loosed on the voting public, at least, not since the NYC Pan Am Heliport fiasco, so I doubt it would be used on a wind turbine where a loose blade would almost certainly cause a lawsuit.

As it happens the system was never deployed on helicopters either. Getting both opposed blades to detach simultaneously (or at all) was a problem that could result in either a diced pilot or the helicopter thrashing itself to pieces. Another correspondent has ponted out the problem of having pyrotechnics sharing space with lightning. Nothing worse than your helicopter shedding a pefectly good rotor in a storm, I imagine. Then, of course, many helicopters do not have symetrically opposed rotor blades - the Sikorsky Sea King and its brethren spring to mind.

What this has to do with wind turbines escapes me, so I'll stamp it with Paris.

@Anonymous Coward with the post about nuke plants...

You really need to take Three Mile Island out of your list of accidents that caused "permanently damaged the gene pool causing birth defects and cancers not only then, now but into the future!" There was very little radiation released from TMI and the containment vessel was never breached in any way. The other reactor at TMI (TMI-1) is still being operated TO THIS DAY.

Here is a quote from the U.S.N.R.C. on the incident:

"Detailed studies of the radiological consequences of the accident have been conducted by the NRC, the Environmental Protection Agency, the Department of Health, Education and Welfare (now Health and Human Services), the Department of Energy, and the State of Pennsylvania. Several independent studies have also been conducted. Estimates are that the average dose to about 2 million people in the area was only about 1 millirem. To put this into context, exposure from a full set of chest x-rays is about 6 millirem. Compared to the natural radioactive background dose of about 100-125 millirem per year for the area, the collective dose to the community from the accident was very small. The maximum dose to a person at the site boundary would have been less than 100 millirem."

Plugged into the mains?

Perhaps someone decided to wire the generator into a transformer, upped the volts, to spin it out of control? Of course they didn't, but anyone who's seen those "The Thick of It" Christmas specials from 2006 will know what I mean. (The Opposition minister was forced by his party leader into buying a wind turbine to install on the roof of his house. He commented that it was costing him a fortune in leccy bills to keep the thing rotating...)

Title

Wo... wo..

"obviosuley you never played with lego moters as a child

if one of the waight matched blades gos the uneven spinwill cause it all to disgentrage v soon after cos of thje exisive speen the energy involved made v soon to be undecitable with the footage we have"

> Why is that van parked so close to the wind turbine

> Why is that van parked so close to the wind turbine when they knew it was going to fail? In the second video, you can see a big poof of dirt right at the moment of failure, and it appears pretty close to the van. After that, it looks like the support tower for the turbine falls pretty close to the van as well.

They probably realised they couldn't fix it and decided to, erm... vacate the area. If I was a reasonable distance from that and noticed the van was next to it then thats just to bad. No way am I going to get any closer to it!

I don't even understand why we have wind farms

Windmill and solar power is dangerous!!!

We must replace them all with atomic reactors RIGHT NOW! as the people who stand to make billions out of their construction tell us that they'll NEVER go wrong!! As for those deadly solar panels!!!!! ;-))

slow motion

Chernobyl

You should remember that the reason the Chernobyl went Bang! is because some stupid technicians ran an experiment without proper precautions. Like not fixing the brakes on a wind turbine in time = human stupidity.

Eggbeaters and Engineering Economics

A few points, from one who used to work in the wind power industry.

1. Wind turbines must be made strong enough to survive peak wind speeds (while safely feathered and shut down), but they only generate power (and thus economic return) on the basis of the average wind speed over time. Ideal wind power conditions = steady, low-gust wind conditions. It is simply impossible to build wind turbines that can generate power in all wind conditions; you must make serious design tradeoffs to make the mill survivable in the real world, to say nothing of making economic break-even. Failures like this are a fact of life, like air crashes. You can minimize but never eliminate them.

2. Vertical-axis turbines like those in Tehachapi have another serious potential defect; if you gang up a bunch of them close together (as in a windfarm), the rotors tend to become aerodynamically synchronized. "So what?" I hear you ask. The 2-bladed models only genenerate power during part of the blades' rotation (none when the blades are straight upwind/downwind), so the power output has cyclic peaks and nulls. If ALL the turbines are in sync, the ENTIRE array will have a massive cyclic variation in output every few seconds or so. Power grids don't like generating plants whose output exhibits megawatt-size variation every second or two...

3. The variable-speed GE turbines weren't invented by GE, but by a company they bought at the Enron fire-sale. It was originally US Windpower. My colleagues...

4. From the outside, and not knowing the details, it looks like the machine lost its power-grid connection at full speed and simultaneously had a failure of the turbine controller (not unlikely if a big power-grid spike or nearby lightning strike popped a breaker and scrambled the controller's brains). At that point, only mechanical failsafes would be operable, and emergency shutdown from full speed is the most demanding scenario for those systems.

Hence, a single mechanical failure (the failsafe braking/feathering device) at the wrong time (loss of grid connection and addled controller at full speed and load) could cause such an event.

My daft ex

On a drive to Birmingham a few years back, we all marvelled at the spiining farms on the banks of the motorway. Said ex comments... "wow, look at those, but why do they need them here?" Upon realising the woman was going to gaff pretty badly, I said "why do you ask, it's perfectly breezy here", she replys, "well, I can understand why they have them in places like spain, keeping the villages cool, but it's fucking freezing here already"

This from the same woman who asked me how construction cranes travell under road bridges...

I don't think I have to give a reason as to why we are no longer courting.

Re: My daft ex

I bet if you told her the theory of "Dark Suckers" (google for it) either her head would go bang trying to comprehend that light bulbs don't produce light but actually suck the darkness out of the air, or she'd be left believing it was true for the rest of her life.